The present invention relates to a controller for an internal combustion engine and a method for controlling an internal combustion engine.
Japanese Patent Application Publication No. 2012-57492 describes an example of a controller executing perturbation control (dither control) so that in response to a warm-up request (temperature increase request) of a catalyst device (catalyst), the air-fuel ratio in some of a plurality of cylinders is set to be richer than the stoichiometric air-fuel ratio and the air-fuel ratio in the remaining cylinders is set to be leaner than the stoichiometric air-fuel ratio.
Purge control that is known in the art draws fuel vapor into an intake passage from a fuel tank storing fuel.
When performing dither control, a difference is produced between the air-fuel ratio in a rich combustion cylinder and the air-fuel ratio in a lean combustion cylinder. Thus, it is difficult to set the air-fuel ratio so as to avoid unsatisfactory combustion as compared with when controlling the air-fuel ratio in every one of the cylinders. When performing purge control, fuel vapor is not always uniformly distributed to the cylinders. This may result in the air-fuel ratio differing between cylinders. Thus, when performing dither control during purge control, the combustion deterioration tendency resulting from dither control will further increase the difference in the fuel vapor distributed between cylinders by purge control.